The selection of polymeric material in more demanding, corrosive, harsh chemical, high-pressure and high-temperature (HP/HT) environments, such as notably in oil and gas downhole applications, in particular in deep see oil wells, is of ultimate importance as it implies that said polymeric materials need to possess some critical properties in order to resist the extreme conditions associated with said environments.
It should be mentioned that in these extreme conditions the polymeric materials are exposed in a prolonged fashion to high pressure, e.g. pressures higher than 30,000 psi, high temperatures, e.g. temperatures up to 260° C., and to harsh chemicals including acids, bases, superheated water/steam, and of course a wide variety of aliphatic and aromatic organics. For example, enhanced oil recovery techniques involve injecting of fluids such as notably water, steam, hydrogen sulfide (H2S) or supercritical carbon dioxide (sCO2) into the well. In particular, sCO2 having a solvating effect similar to n-heptane, can cause swelling of materials in for instance seals, which affect consequently their performance. Polymeric materials having too low glass transition temperatures (Tg) relative to the high temperature in HP/HT applications will suffer from being weak and susceptible to high creep in these HP/HT applications. This creep can cause the seal material made of said polymeric material to no longer effectively seal after prolonged exposure at temperature which are 20 or more ° C. above their Tg.
Thus, properties such as maintaining mechanical rigidity and integrity (e.g. yield/tensile strength, hardness and impact toughness) at high pressure and temperatures of at least 250° C., good chemical resistance, in particular when exposed to CO2, H2S, amines and other chemicals at said high pressure and temperature, swelling and shrinking by gas and by liquid absorption, decompression resistance in high pressure oil/gas systems, gas and liquid diffusion and long term thermal stability need to be considered in the selection of appropriate polymeric materials for HP/HT applications.
Thus said polymeric materials need at least to possess a high glass transition temperature.
The utility of aromatic sulfone ether polymers in applications combining high thermal and chemical exposure has been limited due to the fact that said aromatic sulfone ether polymers are large amorphous materials and are therefore very limited in their chemical resistance. Semi-crystalline aromatic sulfone ether polymers are extremely rare.
Staniland reports notably in Table 1 of Polymer Preprints, American Chemical Society, Division of Polymer Chemistry, 1992, 33(1), pages 404-405, some crystalline polyethersulphone polymers having high transition glass temperatures (Tg) of above 200° C. and having melting temperatures of below 400° C. (e.g. Structures 1-4 and 7). The author is in particular referring to the polyethersulphone polymer of structure 4 described therein (i.e. —OØØØOØSO2Ø—, being understood that Ø is Ph or a phenyl group) derived from 4,4′ dichlorodiphenyl sulfone (DCDPS) and dihydroxyterphenylene, which has a Tg of 251° C. and a Tm of 359° C. Said polyethersulphone polymer of structure 4 was already earlier disclosed by the same author in Bulletin des Societes Chimiques Belges, 1989, 98 (9-10), pages 667-676. FIG. 6 of this paper shows notably a DSC (differential scanning calorimetry) scan of the polyethersulphone polymer of structure 4.
Said polyethersulphone polymer of structure 4 also disclosed in EP 0 383 600 A2, in particular, examples 1 and 2 describe the reaction of dichlorodiphenylsulfone (DCDPS, e.g. example 1) or difluorodiphenylsulfone (DFDPS, e.g. example 2) with 4,4″-terphenyl-p-diol (i.e. HO-Ph-Ph-Ph-OH, also called 4,4″-dihydroxyterphenylene). Said aromatic polymers described in example 1, respectively example 2 have a high transition glass temperature (Tg) of 241° C., respectively 251° C., a Tm melting point of 385° C., respectively 389° C., and a reduced viscosity (RV) measured at 25° C. on a solution of 1.0 g of polymer in 100 cm3 H2SO4 of 0.27 (dL/g), respectively 1.40 (dL/g). As will be mentioned more in detail below, this example yielded a polymer with a Mn of about 13,000-14,000 for polyethersulphone polymer of structure 4 when measured by a GPC method as described below. It is known that thermosets due to their three dimensional network of bonds (i.e. cross-linking) are suitable to be used in high temperature applications up to the decomposition temperature. However, one of the drawbacks is that they are more brittle.
Semi-crystalline polymers when crystallizing from the melt can crystallize in crystals of different structure. Mostly they can form lamellae of different thicknesses, which exhibit different melting temperatures. The fraction of crystals with thinner lamellae (i.e. imperfect crystals) melts at a lower temperature than the thicker lamellae. The presence of these two populations of crystals in general leads to the observation of a double melting endotherm (i.e. two peak melting temperatures) in the DSC. The lower melting temperature of these crystals in general limits the retention of mechanical properties above the Tg. Therefore, the difference between the first melting endotherm and the Tg advantageously should be as high as possible.
In view of all the above, there is still a current shortfall in the art for polyarylene ether sulfone (PAES) polymeric materials having good stiffness and ductility, good chemical resistance, high thermal resistance (e.g. Tg>230° C.), long term thermal stability, useful highest Tm between 360° C. and 420° C., and in particular very useful gap between the first melting endotherm and the Tg and thus said compositions can be particularly useful HP/HT applications requiring a very good chemical resistance.